1. Field of the Invention
This invention is directed to apparatus for fastening and sealing sheets of construction material placed in edgeabutting relation.
The widespread and growing use of construction material in sheet form in all phases of the construction industry has necessitated the development of improved apparatus for fastening together the sheets. Typically, the sheets are positioned over an underlying frame structure with the edges of adjoining sheets abutting to form a joint. In many applications the spacing of the underlying frame members is determined by the dimensions of the sheets so that the joints can be positioned directly over a frame member and so that the sheets can be fastened to the frame structure at the joint locations.
The use of construction materials in sheet form has not been confined to interior applications, and with the development of suitable lightweight weather-proof coatings, the use of sheet material in the fabrication of exterior walls and roofdecks has become commonplace. An example of such sheet material appears in U.S. patent application Ser. No. 702,966. Such exterior applications, however, have required that the fastening apparatus perform a sealing function as well as withstand the additional loadings caused by wind forces and forces induced by thermal expansion and contraction.
2. Description of the Prior Art
U.S. Pat. Nos. 3,320,707 and 3,339,329 to Berg typify apparatus currently used in the construction industry for fastening and sealing sheet material placed in edgeabutting relationship. The apparatus of Berg U.S. Pat. No. 3,320,707 includes a deformable sealing pad, an overlying metal strip, and screws passing through the strip and pad into the underlying frame for forcing the pad into the joint formed by the lipped abutted sheets thereby capturing the sheets. A major problem with such a sheet material fastening device is that, although the metal strip gives the superior hold-down performance needed for exterior applications, the exposed metal acts as an efficient, but unwanted, conductor of heat energy through the joint and past the wall or roof structure. During hot weather this conduction path can result in a significantly increased air conditioning load, while heat losses during the winter months will be reflected in greater heating costs. Such a fastening device, then, is counter-productive, inasmuch as the corresponding sheet materials, especially those intended for roofdeck applications, are usually fabricated for maximum insulating properties.
Also, the direct exposure of metal parts to weathering can lead to corrosion which would necessitate maintenance at unacceptably short intervals during the life of the structure. Such corrosion can be particularly troublesome if dissimilar metals are used for the metal strip and the screws where the galvanic action can greatly accelerate the corrosion rate possibly causing a premature loss of hold-down capability.
Thus a fastener utilizing an unexposed metal strip overlying the edges of the abutted sheets for superior holddown performance but without the attendent heat conduction and corrosion problems of conventional devices would be highly desirable.
With respect to the required sealing function, fasteners such as shown in Berg U.S. Pat. No. 3,320,707 depend upon deformation of the underlying pad against the sheet edges to effect the primary moisture seal in exterior applications. Such as dependency is not altogether satisfactory as deterioration of the pad material and lateral movements in the sheet material caused by thermal expansion and contraction can substantially diminish the sealing effectiveness of such conventional fasteners. Modifications of current fastener configuration such as shown in FIG. 4 of Berg U.S. Pat. No. 3,320,707 and FIG. 3 of Berg U.S. Pat. No. 3,339,329 have attempted to maintain positive contact between the pad member and the exterior facing surfaces of the sheets in an effort to improve the fastener's sealing performance. The aforementioned modifications generally consist of extending the overlying metal or plastic hold-down strip beyond the channel formed by the abutted sheets and by providing that a part of the pad member underlie these extensions to act as a gasket.
These aforementioned modifications are far from being totally satisfactory for several reasons. First, the extending portions of the hold-down strip must be made relatively stiff to compress the underlying pad. The force required to compress these outlying pad portions is unavailable to compress the pad directly over the joint resulting in a decrease in the localized clamping pressure. Decreases in the localized clamping pressure can result in unacceptable lateral movement of the sheets during wind-induced flexing.
Second, the required stiffness of the hold-down strip extensions prevents these appendages from adequately conforming to sheet thickness variations (waviness) along the joint. Portions of the pads underlying the "low spots" may remain uncompressed and provide leakage paths past the intended secondary moisture barrier.
Therefore, a fastener-sealer for edge-abutted sheets of construction material that could accommodate variations in panel thickness without significantly decreasing the localized clamping pressure as is accomplished by the invention, to be described hereafter, would be highly desirable and would certainly find immediate acceptance in the construction industry.
Additional advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practices of the invention. The advantages of the invention may be realized and attained by means and instrumentalities and combinations particularly pointed out in the appended claims.